Processes for producing monolithic porous carbon disks from aromatic organic precursors

ABSTRACT

Disclosed are processes for producing monolithic and metal doped monolithic porous carbon disks from prepolymer organic precursors in the powder form composed of either or both polyimide and polybenzimidazole. The powders are consolidated (compressed) into disks and then pyrolyzed to form the desired porous carbon disk. Porous carbon-carbon composite disks are also prepared by adding carbon to the prepolymer organic precursors.

This is a continuation-in-part of U.S. application Ser. No. 10/919,450,filed Aug. 16, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the preparation of precursors composedof either or both polyimide and polybenzimidazole as organic precursorsfor producing monolithic porous carbon with density less than or equalto 1.0 g/cc; and the processes for producing monolithic porous carbonfrom either or both polyimide and polybenzimidazole precursors in thepowder form. The present invention further relates to the processes forproducing monolithic porous carbon derived from either or both polyimideand polybenzimidazole precursors having one or more than one metalsdispersed therein. The present invention even further relates to theprocesses for producing carbon-carbon composite prepared from precursorscomprising either or both polyimide and polybenzimidazole and activatedcarbon in the form of powders and/or fibers.

2. Description of Related Art

Monolithic porous carbon, which possess interpenetrating pore structure,high density, high surface area, suitable pore size, and well definedpore size distribution, are highly desirable as electrode materials forlithium batteries, electrochemical capacitors, fuel cells, as well asother electrochemical devices. The following description will bedirected to disk products although it will be understood that other suchproducts can be made from the porous carbon.

One approach to produce monolithic porous carbon disk is through sol-geltechnologies. The sol-gel technology generally consists of preparationof gels from solution, drying the gel while minimizing the gelshrinkage. The pyrolysis of thin gel films yields porous monolithiccarbon disks. RF carbon aerogel currently in the market as electrodematerial for supercapacitors is derived from resorcinol and formaldehydeorganic precursors. RF carbon aerogel provide high surface area andnarrow pore size distribution. Yet, the potential market of RF carbonaerogel as electrode and material for ultracapacitors andsupercapacitors is severely limited by the low operating voltage of thecapacitor (<=5V) and high manufacturing cost of monolithic RF carbonaerogel materials.

Another approach to produce monolithic porous carbon disks is frompowders of porous polymeric precursors by compressing them into amonolith disk followed by pyrolysis. There are 2 obstacles in thisapproach. One is the compressibility of the polymer precursor and theother is the difficulty in retaining interpenetrating network of thepores during the compression process. U.S. Pat. No. 6,544,648 disclosesa process for making monolithic carbon disks by compressing carbon blackpowder with high surface area under vacuum at temperatures at or beyond800° C. and a pressure at or beyond 3000 psi. This approach producescarbon disks with more undesirable micro-pores with pore diameter lessthan 2 nm than the ones by the sol-gel approach. The compression ofcarbon powder under vacuum at 800° C. displays severe technicalchallenges and high manufacturing costs.

Yet, another approach to produce monolithic porous carbon is from carbonblack powder consolidated in a matrix of a carbonized synthetic resin.U.S. Pat. Nos. 5,776,633; 5,172,307; and 5,973,912 described processesof producing such porous carbon-carbon composites. The synthetic resinis phenolic resin in the patents. Although this approach has the meritof low cost by using inexpensive carbon black powder it has thedifficulty in retaining open pores of synthetic resin, thus reducing theefficiency of pore surface area.

Bearing in mind the problems and deficiencies of prior art, it istherefore an object of the present invention to provide monolithicporous carbon disks with high surface area, high pore volume, highsurface activity, well defined pore structure and morphology, and goodmechanical properties. It would also be desirable to provide a processfor producing such monolithic porous carbon disks with significantlylower cost as compared to the ones currently in the market.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

SUMMARY OF THE INVENTION

The present invention provides processes for producing monolithic porouscarbon, e.g., disks, from a group of aromatic organic precursorscomprising either or both polyimide or polybenzimidazole. The processesinclude the steps of: (1) preparation of the organic precursors in thepowder form; (2) consolidation of the powders into a monolith; (3)pyrolysis producing a monolithic porous carbon product such as a disk.

The present invention further provides processes for producingmonolithic porous carbon disks doped with transition metals from a groupof aromatic organic precursors comprising either or both polyimide orpolybenzimidazole and metallic compounds. The processes include thesteps of: (1) preparation of the precursors in-situ doped with metalliccompounds in the powder forms; (2) consolidation of the powders into amonolith; (3) pyrolysis producing monolithic porous carbon product suchas a disk.

The present invention even further provides processes for producingporous carbon-carbon composite from the precursors of this invention andcarbon in the forms of powders, or fibers, or nanotubers, or bulky balls(C60, or C70, or others), or fullerenes, or a mixture thereof.Preferably, the carbon that is used in the present processes isactivated carbon powder and activated carbon fiber. The processesinclude the steps of: (1) preparation of the precursors either in thepowder form or a viscous solution; (2) blending together the carbon andthe precursor in which the case of the solvent is removed after mixing;(3) consolidation of the mixture into a monolith; (4) pyrolysisproducing a porous carbon-carbon composite.

The organic precursors of this invention have nitrogen-containingheterocyclic structures that connect monomer units into rod-likemolecular chain structures with few flexible links or hinges. The chainarchitecture of the precursors consists of either linear chains, or athree-dimensional network, or hyberbranched chain structure. One groupof the precursors comprises polyimide with imide group in the molecularstructure. Another group of the precursors comprises polybenzimidazolewith benzimidazole group in the molecular structure. Yet, another groupof the precursors comprises both polyimide and polybenzimidazole withboth imide and benzimidazole groups in the molecular structure.

The monolithic porous carbon disks produced from this invention can befurther reinforced by fibers or fiber pads or other additive byincorporating fibers, inorganic or organic particles, fiber pads, orother additives during the compression molding process.

The precursor powders may be further assembled with other additives inaddition to carbon before consolidation into a monolith. Such additivesinclude transition metal oxide powders, organic particles, inorganicparticles, graphite fibers or flakes, metal fibers, porous substratesincluding membranes, metallic meshes, carbon cloth, carbon felt, foams,and polymeric resins, such as phenolic resins and commercial polyimideresins.

The precursors prepared from the aromatic organic monomers of thisinvention may comprise other components in the molecular chainstructure, such as polybenzimidazole, polyamide, polyetherimide,siloxane, or silica, but have the polyimide and aromatic organiccomposition preferably greater than or equal to 50% by weight.

The polyimide and polybenzimidazole may be represented by the formulas:

-   -   wherein A1 and A4    -   represent difunctional phenyl, difunctional biphenyl, an        optionally substituted difunctional aryl, optionally substituted        difunctional alkylene, an optionally substituted difunctional        heteroaryl, or a combination thereof;    -   wherein A2 and A5 represents tetra functional phenyl, biphenyl,        an optionally substituted tetra functional aryl group, or an        optionally substituted heteroaryl group;    -   wherein A3    -   represent multifunctional phenyl with functionality more than or        equal to 2, multifunctional biphenyl with functionality more        than or equal to 2, an optionally substituted multifunctional        aryl with functionality more than or equal to 2, optionally        substituted multifunctional alkylene with functionality more        than or equal to 2, an optionally substituted multifunctional        heteroaryl with functionality more than or equal to 2, or a        combination thereof;        n1, n2 and n3 are greater or equal to 1; and (y+2) are more than        or equal to 2.

One application of this invention is to provide a novel carbon electrodefor use in electrochemical capacitors, batteries, and fuel cells.

Another application of this invention is to provide a novel composite ofcarbon and transition metal oxides, such as MnO2, as an electrode foruse in lithium batteries or hybrid—battery/electrochemical capacitorsystems.

Another application of this invention is to provide a catalytic carbonsupport for use in fuel cells and electrochemical water purificationsystems.

While the present invention has been particularly described, inconjunction with a specific preferred embodiment, it is evident thatmany alternatives, modifications, and variations will be apparent tothose skilled in the art of the foregoing description. It is thereforecontemplated that the appended claims will embrace any suchalternatives, modifications, and variations as falling within the truescope and spirit of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel and the elementscharacteristic of the invention are set forth with particularly in theappended claims. The figures are for illustration purposes only and arenot drawn to scale.

The invention itself, however, both as to organization and method ofoperation, may best be understood by reference to the detaileddescription which follows taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is a cyclic voltammetry (CV) graph of Example 1 showing C(F/gram) versus voltage at a scan rate of 5 mV/sec.

FIG. 2 is a cyclic voltammetry (CV) graph of Example 2 showing C(F/gram) versus Voltage at a scan rate of 5 mV/sec.

FIG. 3 is a cyclic voltammetry (CV) graph of Example 3 showing C(F/gram) versus Voltage at a scan rate of 5 mV/sec.

FIG. 4 is impedance data of Samples 9a and 9b at 0.75 V bias level withthe sulfuric acid electrolyte. (-black) from Sample 9a and (-red) fromthe capacitor with Sample 9b.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In describing the preferred embodiment of the present invention,reference will be made herein to FIGS. 1-4 of the drawings in which likenumerals refer to like features of the invention.

Detailed Description of the Invention

In a first aspect, the present invention provides processes forproducing monolithic disks comprising either or both polyimide andpolybenzimidazole as organic precursors for producing monolithic porouscarbon which have surface area at or above 500 m²/gram and sufficientlyhigh mechanical strength.

The aromatic monomers for preparing polyimide precursors of thisinvention are preferably selected from one of the following groups:aromatic dianhydride, aromatic diamine, and as an option, an aromaticpolyamine compounds with amine functionality beyond 2; or aromatictetracarboxylic acids, aromatic diamine, and as an option, an aromaticpolyamine compounds with amine functionality beyond 2; or ester(s) ofaromatic tetracarboxylic acids, aromatic diamine, and as an option, anaromatic polyamine compounds with amine functionality beyond 2; oraromatic dianhydride, aromatic isocyanates including diisocyanate andpolyisocyanate with functionality beyond 2.

The aromatic monomers for preparing polybenzimidazole precursors arepreferably selected from one of the following monomer groups: aromaticdialdehydes and aromatic tetraamines; or diesters of aromaticdicarboxylic acids and aromatic tetraamines; or aromatic dicarboxylicacids and aromatic tetraamines.

The precursors comprising either or both polyimide and polybenzimidazolecan preferably be synthesized from the monomers either in the presenceof a solvent or in the melt state by the following procedures:

Procedure 1

-   -   Admixing all the ingredients in the presence of a solvent. The        solvent is removed by distillation, assisted by vacuum if it is        necessary to form a homogeneous mixture in the powder form.        Further chemical reactions to produce un-fusible and un-meltable        high molecular weight polymeric materials proceed after solvent        removal or even after consolidation compression molding of the        powders into a monolith such as a disk.

Procedure 2

-   -   Carrying out the condensation reaction of the aromatic monomers        in the solution to produce precursors as a precipitate in the        forms of either precipitate or gel. The precipitate could be        either a precipitated powder or a precipitated film onto another        solid substrate. The solvent in the precursors is removed by        distillation, assisted by vacuum if it is necessary. The        precursors are further ground into fine powder or porous        particles, filtered through a sieve if it is necessary.

Procedure 3

-   -   Heating the aromatic organic precursors into the melted state        with stirring to form precursors in the solid form. Sometimes,        evaporation of byproducts, such as a low molecular weight        alcohol or water, produces foams instead of dense solid. The        precursor is further ground into fine powder or porous        particles, filtered through a sieve if it is necessary.

The polyimide precursors are preferably condensation products ofaromatic diamines and aromatic tetracarboxylic dianhydride, or aromaticdiamines and tetracarboxylic acids, or aromatic diamines and ester(s) oftetracarboxylic acids, or aromatic isocyanates and aromatictetracarboxylic dianhydride. As an option, a small amount of polyaminecompounds with amine functionality greater than two takes the place ofsome of the aromatic diamine to introduce chemical cross-links to thepolyimide precursors. Therefore, polyimide precursors may possess linearmolecular structure, or a hyper-branched molecular structure, or athree-dimensional network molecular structure. The synthesis ofpolyimide precursors generally proceeds in the synthesis of poly(amicacids) and then imidization to form polyimide.

Using the monomers of aromatic amines including diamines and polyaminecompounds and acids or ester(s) of tetracarboxylic acids the synthesisof polyimide precursors can be carried out according to any ofProcedures 1 to 3. In Procedure 1, the monomers and other additives aredissolved in a solvent to form a clear solution. The precursors in theform of fine powders are either a homogeneous mixture of monomers or amixture of low molecular weight oligomers of polyimide and poly(amicacids). In Procedure 2, the monomers and other additives are dissolvedin an organic solvent. The reaction is carried out with a normalagitation at or above 100° C., preferably at or above 150° C., toproduce polyimide precipitate. The polyimide precursors are in the formof either precipitated powder or gels. The solvent is removed from theproduct by distillation, assisted by vacuum if it is necessary. InProcedure 3, preferably, the esters of tetracarboxylic acids andaromatic amines are the monomers of choice. The condensation reaction atmolten state of monomers releases phenol or an alcohol molecule in thegas phase to produce rigid polyimide foams. The product is furtherground to produce polyimide powder.

Using the monomers of aromatic dianhydride and aromatic amines includingdiamines and polyamines the synthesis of polyimide precursor is carriedout according to Procedure 2 in two steps: synthesis of poly(amic acids)and imidization to form polyimide. The synthesis of poly(amic acids) isconducted by dissolving monomers and other additives in an organicsolvent at ambient temperature with a normal agitation for a time periodfrom several hours to overnight to yield product in the forms of eitherprecipitated powder or viscous liquid solution or gels. The imidizationof poly(amic acids) to form polyimide is carried out by either chemicalimidization at ambient temperature or thermal imidization at elevatedtemperatures.

The chemical imidization is conducted by addition of dehydrating agentsto poly(amic acids). In the cases of poly(amic acids) in the form ofprecipitated powder, preferably, dehydrating agents are added before thereaction solvent is removed from the system. In the cases of poly(amicacids) in the form of viscous solution, the addition of dehydratingagents to poly(amic acids) solution is carried out in such a way thatthe reaction at ambient temperature yields polyimide precipitate. Thesolvent is removed from the polyimide precipitate by distillation.

The dehydrating agents consists of either an acid anhydride or a mixtureof an acid anhydride and an organic base. Preferred acid anhydridesinclude acetic anhydride, propionic anhydride, n-butyric anhydride,benzoic anhydride, and trifluoroacetic anhydride. Preferred organicbases include optionally substituted mono-, di-, trialkylamines, andoptionally substituted pyridines.

The thermal imidization is conducted at elevated temperatures.

In the cases of poly(amic acids) in the form of precipitated powder, thesolvent is removed by distillation followed by a thermal imidization ofpoly(amic acids) powder at a temperature in the range of 50° C. to 500°C. preferably in the range of 100° C. to 400° C. and preferably underprotection of an inert gas, such as nitrogen or argon. In the cases ofpoly(amic acids) in the form of viscous liquid solution or gels theimidization is conducted at elevated temperatures in the range of 50° C.to 400° C., preferably in the range of 100° C. to 250° C. to producepolyimide in the form of precipitated powder. The solvent is removed bydistillation, assisted by vacuum if it is necessary.

Using aromatic dianhydride and aromatic isocyanate includingdiisocyanate and polyisocyanate as the organic precursor the synthesisof polyimide precursors is preferably carried out according toProcedure 1. In this procedure, the monomers and additives are admixedat ambient temperature in the presence of preferably a dipolar aproticorganic solvent. The solvent removal produces a homogeneous mixture inthe powder form.

Although not exclusive to the other synthetic procedures, preferably,polyimide precursors are prepared from aromatic monomers oftetracarboxylic dianhydride, aromatic diamine, and optionally, apolyamine compound according to Procedure 2 using thermal imidizationmethod. In this procedure, the reaction of monomers and other additivesare conducted in an organic solvent, such as dimethylacetamide (DMAc),at ambient temperature with agitation for a period of time. Temperatureof the reaction system is then raised to the range of 130° C. to 200°C., preferably in the range of 150° C. to 180° C. to produce polyimideas precipitate. The solvent is distilled off to produce the driedpolyimide precursor powder.

The polybenzimidazole precursors are preferably condensation products ofaromatic tetraamines and aromatic esters of dicarboxylic acids, oraromatic tetraamines and aromatic dialdehyde. The synthesis proceedseither in the molten state of monomers or in the presence of a solvent.

Using aromatic tetraamine and aromatic dialdehyde as aromatic monomersthe synthesis of polybenzimidazole is carried out according to Procedure2 in two-stages: synthesis of poly(azomethines) as intermediate productin the presence of an organic solvent and synthesis ofpoly(benzimidazole). In this procedure, the reaction of the monomers inan organic solvent is carried out at temperatures in the range of −30°C. and ambient temperature to produce poly(azomethines) in the forms ofeither precipitated powder or viscous liquid solution. Further reactionat an elevated temperature in the range of 50° C. to 350° C., morepreferably in the range of 100° C. to 250° C., convertspoly(azomethines) to polybenzimidazole. The solvent is removed from thesystem when the product precipitated from the solution either before orafter second stage reaction at elevated temperatures.

Using the monomers of aromatic tetraamine and esters of dicarboxylicacids the synthesis of polybenzimidazole proceeds preferably accordingto Procedure 3 in the molten state of the monomers although notexclusive to the synthesis in the presence of a solvent. The reactionsare conducted at or above melting temperatures of the monomers withstrong agitation and in such conditions that side products of phenol, orwater, or an alcohol in the gas phase are released from the system toproduce the product in foams. The products are crushed and furtherground to produce polybenzimidazole precursors in the form of porouspowder.

The precursors comprising both polyimide and polybenzimidazole segmentsin the molecular structure can be prepared preferably in the presence ofan organic solvent. The synthesis can be conducted by eithersynthesizing one precursor of either polyimide or polybenzimidazolebefore adding the monomers for the other precursor to the reactionsystem. Or the reactions of polyimide and polybenzimidazole are carriedout separately before combining two reactions into one reaction system.Or two sets of the monomers are mixed together simultaneously in thesame reaction solution when the reaction conditions are compatible. Yet,such mixing would be generally prohibited if a relatively large amountof flexible amide links were introduced to the molecular chain structureso as to reduce the glass transition temperature of the materialsignificantly.

An alternative approach to prepare monolithic porous carbon disks fromprecursors comprising both polyimide and polybenzimidazole is mixingboth powders of polyimide and polybenzimidazole precursors togetherduring the process of consolidating the powders into a monolith disk.

As an option, the precursor powders comprising either or both polyimideand polybenzimidazole are further broken down to smaller particle sizeby a shear stress and filtered through a sieve if it is necessary. Thepreferred particle size of precursors for the purpose of compressionmolding is in the range of 1 μm to 300 μm, more preferably in the rangeof 5 μm to 75 μm, even more preferably in the range of 10 μm to 50 μm.

As another option, the precursor powder comprising either or bothpolyimide and polybenzimidazole in the powder form is further thermallyannealed at elevated temperatures before consolidating into a disk. Theannealing is conducted in a temperature range of 50° C. to 600° C., morepreferably in the range of 50° C. to 500° C. for a time period between20 minutes to 2 hours under vacuum or under protection of argon ornitrogen atmosphere.

In a second aspect, the present invention provides processes forproducing porous monolithic disks of transition metal doped precursorscomprising either or both polyimide and polybenzimidazole as organicprecursors for producing transition metal doped monolithic porous carbondisks which have surface area at or above 500 m²/gram, sufficiently highmechanical strength, and macrocyclic pyridine structure wherein thetransition metal atoms caged or complexed into to provide catalyticactivities.

In a general procedure, a transition metallic compound in solution isadded to the reaction system or to the dried precursor powder or to thedried disk precursor. The solvent used for dissolving the transitionmetallic compound is preferably the same solvent as the one forpreparing the precursors. Although not exclusive to the addition of themetallic compounds at any stage or any step during preparation of themonolith disk including each synthetic step of the condensation reactionand the consolidation process, preferably, the transition metalliccompounds are added during the early stages of the procedures. Even morepreferably, the transmission metallic compounds are admixed with theorganic precursors in the presence of an organic solvent beforeproceeding with the synthesis of the precursors.

The solvent removal during the synthesis of the precursors comprisingeither or both of polyimide and polybenzimidazole are conducted bydistillation, preferably assisted by vacuum.

Metals suitable for use in the preparation of metal doped monolithicporous carbon of this invention are not limited and may includeelemental metals, organometallic compounds, coordination inorganiccompounds, metal salts or any combinations thereof. The preferred metalsinclude Ti, Zr, V, Nb, Cr, Mo, Mn, Fe, Ru, Co, Rh, Ni, Pd, Pt, Cu, Ag,Zn, Si, Sn, Pb, Sb, Nb, Bi, Hf, Ba, Al, B, P As, Li and combinationsthereof. Exemplary transition metal compounds include cobalt chloride(COCl₂), iron chloride (FeCl₃), nickel chloride (NiCl₂), molybdenumchloride (MoCl₅), hydrogen hexachloroplatinate hydrate (H₂PtCl₆.xH₂O),copper chloride (CuCl₂), tungsten chloride (WCl₆), zirconium chloride(ZrCl₄), cerium nitrate (Ce(NO₃)₃), ruthenium chloride (RuCl₃) andhafnium chloride (HfCl₄).

Typically, the transition metallic compound is present in the precursorin an amount from 0.01% to 20% by weight, or more.

In a third aspect, the present invention provides processes forproducing monolithic porous carbon disks which has a rod density of lessthan or equal to 1.0 gram/cc comprising: producing the organicprecursors in powders comprising either or both polyimide andpolybenzimidazole; consolidation of the powder into a monolith under apressure in the range of 3000 psi to 13000 psi; and pyrolysis underprotection of an inert atmosphere.

In a fourth aspect, the present invention provides processes forproducing monolithic porous carbon having one or more than one metalsdispersed therein, which has a rod density of less than or equal to 1.0gram/cc comprising: powders of transition metal doped precursorscomprising either or both polyimide and polybenzimidazole; consolidationof the porous precursor powders into a monolith preferably at ambienttemperature under a pressure in the range of 3000 psi to 13000 psi. andpyrolysis under protection of an inert atmosphere.

In a general consolidating procedure, the precursor powders are evenlyplaced in a mold or on a supporting substrate such as a fiber pad,before a sufficiently high compression pressure and a sufficient holdingtime are applied to produce a monolith disk with rod density in therange of 0.4 g/c to 1.0 g/c, preferably 0.6 g/cc to 0.95 g/cc.

Pyrolysis of the compressed disks is carried out under protection of aninert gas atmosphere, such as argon, nitrogen or carbon dioxide, at atemperature in the range of 600° C. to 3000° C., more preferably 750° C.to 1500° C. As an option, the inert gas atmosphere may be changed tocarbon dioxide during the pyrolysis, preferably in the later stage ofthe pyrolysis, to further activate the pore surface of the monolithiccarbon disk. The heating rate shall be sufficiently slow as to optimizethe properties of the monolithic carbon.

In fifth aspect, the present invention provides processes for producingporous carbon-carbon composite with a rod density of less than or equalto 1.0 gram/cc from the precursors comprising either or both polyimideor polybenzimidazole and activated carbon in the forms of powder andfiber comprising: blending the precursor, carbon, and other additivesthoroughly; removing the solvent in the mixture in cases that a solventis involved in the mixture; consolidating the mixture into monolithunder pressure conditions as to produce a homogeneous composition withdesired rod density; and pyrolysis under an inert atmosphere forproducing monolithic porous carbon.

In a sixth aspect, the present invention provides processes forproducing porous carbon composites incorporating other additives inaddition to the carbon comprising: blending the organic precursor ofthis invention, carbon, and other additives thoroughly; removing thesolvent in the mixture in cases that a solvent is involved during themixing; consolidating the mixture into monolith under pressureconditions as to produce a homogeneous composition with desired roddensity; and pyrolysis under an inert atmosphere for producingmonolithic porous carbon.

Other additives include metallic compounds, silica, carbon in the formsof powders, fibers, nanotubes, and bulkyballs or fullerences, graphite,metal oxides and metal carbides, polymeric resins in either liquid orpowder forms, such as commercial phenolic resins and commercialpolyimide resins, and mixtures thereof.

The additives can be in the forms of powders, fibers, flakes, liquids,or porous substrates composed of one or more than one kind of fibers,membranes, metallic meshes, and foams.

There are different ways to blend the polyimide precursor, carbon, andother ingredients together. For example in the cases of polyimideprecursors, one way of blending is to thoroughly mix polyimide powderwith the carbon and other additives. Another way is to coat viscoussolution of poly(amic acid) onto carbon and other additives beforeremoving the solvent, then converting poly(amic acids) to polyimides.The present invention is directed in one aspect to simply mixing thepolyimide precursor powder with the carbon and other additives, but isnot intended to be limited to any particular way of blending theprecursor with the carbon as well as other additives.

The organic precursors comprising either or both polyimide andpolybenzimidazole suitable for use in the method of making monolithicporous carbon disks of the present invention can incorporate othercomponents during the synthesis, such as imidazopyrrolone, siloxane,silica, epoxy, bismaleimide, polyetherimide, but have the composition ofpolyimide and/or polybenzimidazole preferably greater than or equal to70% by weight.

Preferred aromatic tetracarboxylic dianhydride, or tetracarboxylicacids, or diester(s) of tetracarboxylic acids monomers suitable for usein the method of making polyimide precursors of the present inventioninclude following dianhydride compounds and their derivatives oftetracarboxylic acids and dialkyl ester(s) of tetracarboxylic acids:pyromellitic dianhydride; pyromellitic tetracarboxylic acids, dialkylester(s) of pyromellitic tetracarboxylic acids and aromatictetracarboxylic dianhydride or tetracarboxylic acids or esters of thetetracarboxylic acids including 3,3′,4,4′-biphenyltetracarboxylic aciddianhydride, 3,3′,4,4′-benzophenone dianhydride, 2,3,6,7-naphthylenetetracarboxylic acid dianhydrides, 1,4,5,8-naphthalene tetracarboxylicacids, 2,2-bis(3,4-dicarboxy phenyl)propane acid dianhydride, andcombinations thereof.

When ester(s) are alkyl esters the alkyl group preferably contains 1 to5 carbon atoms and is more preferably methyl.

Preferred aromatic diamine monomers suitable for use in the methods ofmaking polyimide precursors of the present invention include1,4-phenylene diamine, m-phenylene diamine, 4,4′-diamino-biphenyl, 4,4′and 3,3′-diaminodiphenylmethanes, 4,4′, and 3,3′-diaminobenzophenones,benzidine, 2,6-diaminopyridine, 2,6-diaminonaphthalene,1,4-diaminocyclohexane, 2,4 and 2,6-diaminotoluene, and derivativesthereof (i.e.: substituted diamine having a substituent(s)). The abovediamine monomers may be used alone or as a mixture of two or more ofthem.

Preferred polyamine compounds with amine functionality greater than 2suitable for use in the methods of making polyimide precursors of thepresent invention include 3,3′,4,4′-biphenyltetraamine (TAB),1,2,4,5-benzenetetraamine, 3,3′,4,4′-tetraminodiphenyl ether,3,3′,4,4′-tetraminodiphenylmethane, 3,3′,4,4′-tetraminobenzophenone,3,3′,4-triaminodiphenyl, 3,3′,4-triaminodiphenylmethane,3,3′,4-triaminobenzophenione, 1,2,4-triaminobenzene, their mono-, di-,tri-, or tetra-acid salts, such as 3,3′,4,4′-biphenlyltetraaminetetrahydrochloride, 1,2,4,5-benzenetetraamine tetrahydrochloride,3,3′,4,4′-tetraaminodiphenyl ether tetrahydrochloride,3,3′,4,4′-tetraminodiphenylmethane tetrahydrochloride,3,3′,4,4′-tetraminobenzophenone tetrahydrochloride,3,3′,4-triaminodiphenyl trihydrochloride, 3,3′,4-triaminodiphenylmethanetrihydrochloride, 3,3′,4-triaminobenzophenone trihydrochloride,1,2,4-triaminobenzene trihydrochloride, melamine,2,4,6-triaminopyrimidine (TAP). The acid salts of above compoundsusually exist in the form of hydrated compounds. Any of the abovecompounds may be used either alone or as a mixture of two or more ofthem.

Preferred polyamine compounds with amine functionality greater than 2suitable for use in the methods of making polyimide precursors composedof a three-dimensional molecular structure of the present invention alsoinclude a polyamine oligomer with the formula:

Preferred aromatic isocyanate monomers suitable for use in the methodsof making polyimide precursors of the present invention include1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate,4,4′-diphenylmethane diisocyanate. Any of the above compounds may beused either alone or as a mixture of two or more of them.

Preferred aromatic dialdehyde monomers suitable for use in the methodsof making polybenzimidazole precursors of the present invention includeisophthalaldehyde, terephthaldicarboxaldehyde, phthalicdicarboxaldehyde, and 2,6-naphthalenedicarboxaldehyde.

Preferred monomers of aromatic acids and esters of dicarboxylic acidssuitable for use in the methods of making polybenzimidazole precursorsof the present invention include acids and esters of isophthalic acid,phthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, and2,6-naphthalenedicarboxylic acid. The ester(s) may be alkyl or phenylesters. When ester(s) are alkyl esters the alkyl group preferablycontains 1 to 5 carbon atoms and is more preferably methyl.

Preferred monomers of aromatic tetraamines suitable for use in themethods of making polybenzimidazole precursors of the present inventioninclude 3,3′,4,4′-tetraminobiphenyl (3,3′-diaminobenzidine);1,2,4,5-tetraminobenzene; 1,2,5,6-tetraminonaphthalene;2,3,6,7-tetraminonaphthalene; 3,3′,4,4′-tetraminodiphenyl methane;3,3′,4,4′-tetraminodiphenyl ethane;3,3′,4,4′-tetraminodiphenyl-2,2-propane; and combinations thereof.

Preferred reaction solvents for the synthesis of the precursorscomprising either or both polyimide and polybenzimidazole includeN-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAc),N,N-dimethyl formamide (DMF), tetrahydrofuran (THF), dimethyl sulfoxide(DMSO), acetone, methanol, toluene, chlorobenzene, ethanol, and mixturesthereof.

The monolithic carbon of this invention is suitable for use as anelectrode material in electrochemical capacitors and relatedelectrochemical devices. The porous monolithic carbon of the inventionoffer the advantage of a monolithic structure, high density, highsurface area, and narrow pore size distribution.

EXAMPLES Example 1 Synthesis of Polyimide Precursor withThree-Dimensional Molecular Structure and Carbon Disk Therefrom

Starting monomers: 3,3′,4,4′-biphenyltetraamine (TAB),1,2,4,5-benzenetetracarboxylic dianhydride (PMDA), and1,4-phenylenediamine (PPD).

Solvent: N,N-dimethylacetamide (DMAc).

1.30 gram (0.012 mole) PPD was dissolved in 40 ml DMAc in a flask. Whilestirring, 3.270 gram (0.015 mole) PMDA in the solid form was added tothe reaction system. After PMDA was fully dissolved, 0.3215 gram (0.0015mole) TAB was added to the reaction system. The reaction was carried outat ambient temperature with mechanical stirring until a very viscoussolution, often gel lumps, were formed. The temperature of the reactionwas gradually raised to 150° C. with strong agitation to producepolyimide in precipitated powder form. The solvent was distilled offunder vacuum at 50° C. The powders were further broken down and filteredthrough a 50 micron-sized sieve.

By using a hydraulic press, the polyimide powders were placed in a moldand compressed under pressure of 5000 psi at ambient temperature toproduce a monolithic disk. The monolithic disk was pyrolyzed at 800° C.for 3 hours under protection of nitrogen to produce a monolithic carbondisk. The cyclic voltammetry of the carbon disk at a scan rate of 5 mV/sdisplayed the capacitance of the material at 90 F/gram. See FIG. 1.

Example 2 Synthesis of Polyimide Prepolymer with Three-DimensionalMolecular Structure Doped with 1% Molybdenum by Weight and Carbon DiskTherefrom

Starting monomers and additive: 3,3′,4,4′-biphenyltetraamine (TAB),1,2,4,5-benzenetetracarboxylic dianhydride (PMDA), 1,4-phenylenediamine(PPD), and molybdenum chloride (V) (MoCl5).

Solvent: N,N-dimethylacetamide (DMAc).

1.30 gram (0.012 mole) PPD and 0.135 gram MoCl5 were dissolved in 40 mlDMAc in a flask. While stirring, 3.270 gram (0.015 mole) PMDA in thesolid form was added to the reaction system. After PMDA was fullydissolved, 0.3215 gram (0.0015 mole) TAB was added to the reactionsystem. The reaction was carried out at ambient temperature withmechanical stirring until a very viscous solution, often gel lumps, wereformed. The temperature of the reaction was gradually raised to 150° C.with strong agitation to produce polyimide/MoCl5 in precipitated powderform. The solvent was distilled off under vacuum at 50° C. The powderswere further broken down and filtered through a 50 micron-sized sieve.

The polyimide powders were consolidated at 4500 psi pressure at ambienttemperature to produce a monolithic disk. The monolithic disk waspyrolyzed at 800° C. for 3 hours under protection of a nitrogen toproduce a monolithic carbon disk. The cyclic voltammetry of the carbondisk at a scan rate of 5 mV/s displayed the capacitance of the materialat 210 F/gram. See FIG. 2.

Example 3 Synthesis of Polyimide Prepolymer Doped with 1% Molybdenum byWeight and Carbon Disk Therefrom

Starting monomers and additive: 1,2,4,5-benzenetetracarboxylicdianhydride (PMDA), 1,4-phenylenediamine (PPD), and molybdenum chloride(V) (MoCl5).

Solvent: N,N-dimethylacetamide (DMAc).

1.622 gram (0.015 mole) PPD and 0.135 gram MoCl5 were dissolved in 40 mlDMAc in a flask. While stirring, 3.270 gram (0.015 mole) PMDA in thesolid form was added to the reaction system. The reaction was carriedout at ambient temperature with stirring until a very viscous solutionwas formed. The reaction temperature was raised to 150° C. with strongagitation to produce polyimide/MoCl5 precipitate in precipitated powderform. The solvent was distilled off under vacuum at 50° C. The powderswere further broken down and filtered through a 5-micron-sized sieve.

The polyimide powders were consolidated at 4500 psi pressure at ambienttemperature to produce a monolith. Pyrolysis of the monolith was carriedout at 800° C. for 2 hours under a nitrogen atmosphere and 1 hour undera carbon dioxide atmosphere. The cyclic voltammetry of the carbon diskat a scan rate of 5 mV/s, shown in FIG. 3, displayed the capacitance ofthe material at 200 F/gram.

Example 4 Synthesis of Polyimide Precursor Doped with 1% (by Wt.)Molybdenum in Acetone and Carbon Disk Therefrom

Starting monomers and additive: 3,3′,4,4′-biphenyltetraamine (TAB),1,2,4,5-benzenetetracarboxylic dianhydride (PMDA), 1,4-phenylenediamine(PPD), and molybdenum chloride (V) (MoCl5).

Solvent: acetone

3.270 gram (0.015 mole) PMDA was dissolved in 20 ml acetone. 1.30 gram(0.012 mole) PPD, 0.3215 gram (0.0015 mole) TAB, and 0.135 gram MoCl5were dissolved in 20 ml acetone in a separate flask. The PMDA solutionwas gradually added to PPD/TAB/MoCl₅ solution to produce a whiteprecipitate immediately. The solvent was distilled off and temperatureof the product was raised to 150° C. to convert poly(amic acids) topolyimide in powder form. The powders are further broken down andfiltered through a 50 micron-sized sieve.

The polyimide powder was compressed at 4000 psi pressure at ambienttemperature to produce a monolithic disk. The monolithic disk waspyrolyzed at 800° C. for 3 hours under protection of nitrogen to producea monolithic carbon disk. The cyclic voltammetry of the carbon disk at ascan rate of 5 mV/s displayed the capacitance of the material at 100F/gram.

Example 5 Synthesis of Polyimide Precursor with Three-DimensionalMolecular Structure Doped with 1% Molybdenum by Weight and Carbon DiskTherefrom

Starting monomers and additive: 3,3′,4,4′-biphenyltetraamine (TAB),1,2,4,5-benzenetetracarboxylic dianhydride (PMDA), 1,4-phenylenediamine(PPD), diaminopyridine, and molybdenum chloride (V) (MoCl5).

Solvent: N,N-dimethylacetamide (DMAc).

1.082 gram (0.01 mole) PPD, 0.218 gram diaminopyridine (0.002 mole) and0.135 gram MoCl5 were dissolved in 40 ml DMAc in a flask. Whilestirring, 3.270 gram (0.015 mole) PMDA in the solid form was added tothe reaction system. After PMDA was fully dissolved, 0.3215 gram (0.0015mole) TAB was added to the reaction system. The reaction was carried outat ambient temperature with a normal agitation until a viscous solutionwas formed. The temperature of the reaction was raised to 150° C. withstrong agitation to produce polyimide/MoCl5 in precipitated powder form.The solvent was distilled off under vacuum at 50° C. The powders werefurther broken down and filtered through a 50 micron-sized sieve.

The polyimide powder were compressed at 4000 psi pressure at ambienttemperature to produce a monolithic disk. The monolithic disk waspyrolyzed at 800° C. for 3 hours under protection of nitrogen to producea monolithic carbon disk. The cyclic voltammetry of the carbon disk at ascan rate of 5 mV/s displayed the capacitance of the material at 100F/gram.

Example 6 Synthesis of Polyimide Prepolymer and Porous Carbon Therefrom

Starting monomers: 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA),and 1,4-phenylenediamine (PPD).

Solvent: N,N-dimethylacetamide (DMAc).

1.622 gram (0.015 mole) PPD was dissolved in 40 ml DMAc in a flask.While stirring, 3.270 gram (0.015 mole) PMDA in the solid form was addedto the reaction system. The reaction was carried out at ambienttemperature with stirring until a very viscous solution was formed. Thereaction temperature was raised to 150° C. with strong agitation toproduce polyimide precipitate. The solvent was distilled off undervacuum at 50° C. The powders were further annealed at 300° C. for 30minutes.

The polyimide powders were consolidated at 4500 psi pressure at ambienttemperature to produce a monolith. Pyrolysis of the monolith was carriedout at 900° C. for 3 hours under a nitrogen atmosphere. The cyclicvoltammetry of the carbon disk at a scan rate of 5 mV/s displayed thecapacitance of the material at 80 F/gram.

Example 7 Electrode for Supercapacitor

A supercapacitor was constructed using the carbon prepared according toExample 3 as electrodes. The electrode dimension was 0.81″ in diameterand 0.012″ in thickness. The prototype supercapacitor comprises a pairof carbon electrodes sandwiched between two current collector plates. Amicroporous separator was placed between two electrodes. 38% sulfuricacid electrolyte impregnates the electrodes and the separator before thecurrent plates were sealed by a thermoplastic edge sealant. The resultof characterization is shown in Table 1.

TABLE 1 ESR (Ohm) Normalized Capacitance at 1 kHz C (F) (F/g) (F/cm³)0.32 7.58 203 156

Example 8 Synthesis of Polyimide Precursor Doped with 0.5% Molybdenumand Porous Carbon Therefrom

Starting monomers and additive: 1,2,4,5-benzenetetracarboxylicdianhydride (PMDA), 1,4-phenylenediamine (PPD), and molybdenum chloride(V) (MoCl5).

Solvent: tetrahydrofuran (THF).

3.270 gram (0.015 mole) PMDA was dissolved in 20 ml THF. 1.62 gram(0.015 mole) PPD, and 0.065 gram MoCl5 were dissolved in 20 ml THF in aseparate flask. The PMDA solution was gradually added to PPD/MoCl5solution to produce a white precipitate immediately. The solvent wasdistilled off. The poly(amic acids) powder was converted to polyimide bythermally annealed at 300° C. for 30 minutes.

The polyimide powders were compressed at 4500 psi pressure at ambienttemperature to produce a monolith. The monolith was pyrolyzed at 900° C.for 3 hours under protection of nitrogen to produce a monolithic carbon.The cyclic voltammetry of the carbon disk at a scan rate of 5 mV/sdisplayed the capacitance of the material at 150 F/gram.

Example 9a Preparation of Carbon-Carbon Composite and an ElectrochemicalCapacitor Cell Therefrom

Polyimide precursor: prepared in Example 6.Carbon Black Powder: commercially available carbon black from a naturalsource;Activated Carbon fiber: phenolic resin based carbon fiber.

1.58 gram carbon black powder (66%), 0.68 gram polyimide powder (28%),and 0.14 gram carbon fiber (6%) were blended together by grinding andmixing 0.5 gram mixture was compressed at 6500 psi at ambienttemperature to produce a monolithic disk about 1 mm thick and 2.5 cm indiameter. The disk was pyrolyzed at 800° C. for 3 hours under protectionof nitrogen to produce a porous carbon-carbon composite disk.

Two carbon-carbon composite disks of 0.78 gram with diameter of 2.5 cmand thickness of 1.20 mm were used to assemble a symmetric single cellaccording to the procedure in Example 3. The result of characterizationis listed in Table 2. A Z″ vs. Z′ plot of impedance data is displayed inFIG. 4.

Example 9b A Comparative Electrochemical Capacitor Cell Using CarbonBlack Electrodes

Two carbon disks of 0.77 gram with diameter of 2.5 cm and thickness of1.20 mm were prepared from same carbon black powder as used in Example9a. The disks were used to assemble a symmetric single cell according tothe procedure in Example 3. The result of characterization is listed inTable 2. A Z″ vs. Z′ plot of impedance data is displayed in FIG. 4.

TABLE 2 Normalized ID ESR (Ohm) at 1 kHz C (F) C (F/g) C-C composite0.082 30.25 154 (Example 9a) Control carbon 0.101 22.44 116 (Example 9b)

Example 10 Preparation of Carbon-Carbon Composite Doped with 0.85%Molybdenum and an Electrochemical Capacitor Cell Therefrom

Polyimide precursor: prepared in Example 1.Carbon Black Powder: commercially available carbon black from a naturalsource;Activated Carbon fiber: phenolic resin based carbon fiber;Molybdenum chloride (V) (MoCl5).

0.06 gram molybdenum chloride was dissolved in 3.0 ml methanol. 2.6 gramcarbon black powder was immersed in Mo/methanol solution with stirringfor overnight before methanol was removed by distillation.

1.24 gram Mo doped carbon black powder (61%), 0.665 gram polyimidepowder (33%), and 0.12 gram activated carbon fiber (6%) were blendedtogether by grinding and mixing. 0.5 gram mixture was compressed at 6500psi at ambient temperature to produce a monolithic disk about 1 mm thickand 2.5 cm in diameter. The disk was pyrolyzed at 800° C. for 1.5 hoursunder protection of nitrogen and 1.5 hours under carbon dioxide toproduce a porous carbon-carbon composite disk.

Two carbon-carbon composite disks with diameter of 2.5 cm and thicknessof 1.20 mm were used to assemble a symmetric single cell according tothe procedure in Example 3.

1-28. (canceled)
 29. An electrochemical device comprising at least onecell, said cell comprising: two conductive electrodes; and a porousnon-conductive separator disposed between the two electrodes, anelectrolyte occupying pores of said electrodes and separator, wherein atleast one of said electrodes comprises a monolithic porous carbon or aporous carbon composite; wherein the composite comprises organicprecursor powders; wherein the organic precursor powders comprisepolyimide or polybenzimidazole; and wherein the organic precursorpowders have been compressed and subjected to pyrolysis.
 30. The deviceof claim 29 wherein the cell includes capacitors, supercapacitors,electrochemical-electrolytic hybrid capacitors, hybridbattery/supercapacitor systems, lithium batteries, fuel cells, and othertypes of batteries.
 31. An electrochemical device comprising at leastone cell, said cell comprising: two conductive electrodes; and a porousnon-conductive separator disposed between the two electrodes, anelectrolyte occupying pores of said electrodes and separator, wherein atleast one of said electrodes comprises a monolithic porous carbon or aporous carbon composite; wherein the composite comprises organicprecursor powders and carbon; wherein the organic precursor powderscomprise polyimide or polybenzimidazole; and wherein the organicprecursor powders and the carbon have been compressed and subjected topyrolysis.
 32. The device of claim 31 wherein the cell includescapacitors, supercapacitors, electrochemical-electrolytic hybridcapacitors, hybrid battery/supercapacitor systems, lithium batteries,fuel cells, and other types of batteries.